The present invention relates generally to semiconductor pressure sensor devices, and, more particularly, to a pressure sensor device with a gel filled cavity.
For certain semiconductor devices, such as those that include pressure sensing dies, it is known to apply a pressure-sensitive gel over the pressure sensing die to protect the die while still allowing the die to sense the atmospheric pressure outside of the package.
In some package designs having one or more dies, the dies are placed in a cavity. The gel fills the cavity so that it covers all of the dies as well as any bond wires used to connect the dies to one another and/or to device leads. Unfortunately, due to the surface tension of the gel, when the gel is dispensed into the cavity, the gel adheres to the sides of the cavity and a meniscus is formed such that the top surface of the gel has a concave shape.
FIG. 1 shows a cross-sectional side view of a conventional semiconductor sensor device 10. The sensor device 10 includes a control unit die 12 and a pressure sensor die 14 disposed in a housing. The housing is formed by a lead frame flag 16 upon which the dies 12 and 14 are mounted, lead frame leads or lead fingers 18, and side walls 20. The pressure sensor die 14 is connected to the control unit die 12 with first bond wires 22 and the control unit die 12 is connected to the lead fingers 16 with second bond wires 24. The flag 16, lead fingers 18 and side walls 20 of the housing form a cavity 26 within which the dies 12 and 14 are located. The cavity 26 is partially filled with a gel 28 that covers the dies 12 and 14 and the bond wires 22 and 24, but enables the air/gas pressure surrounding the device 10 to reach the pressure-sensitive active region on the top side of the pressure sensor die 14. The gel 28 protects the dies 12 and 14 and the bond wires 22, 24 from mechanical and environmental damage. The cavity 26 is covered by a lid 30, which has a vent hole 32 that exposes the gel-covered pressure sensor die 14 to ambient atmospheric pressure outside the sensor device 10.
As previously discussed, the gel 28 dispensed into the cavity 26 adheres to the side walls 20 of the cavity 26 and a meniscus is formed such that the top surface of the gel 28 has a concave shape depending on the gel surface tension and cavity side wall roughness. If the curvature of the upper surface becomes too great, then portions of the first bond wires 22 (and possibly even portions of the dies 12 and 14, the second bond wires 24) may become exposed to the ambient atmosphere above the gel 28 as shown in FIG. 1. Exposure of the bond wires 22 and the dies 12, 14 to the ambient atmosphere can result in environmental damage (e.g., contamination and/or corrosion) to the sensor device 10. Accordingly, it would be advantageous to have a structure and process that ensures the bond wires are fully covered with gel.